The present invention relates to a strut device for use in a drum brake, more particularly, to a method of manufacturing an improved strut member, which is a component of the strut device, from a tube material. A strut device of the type shown in FIGS. 1 and 2 which are referred in the brief description of the drawing, is widely employed for the purpose of compensating the increase of the brake gap, an operating gap of the brake shoe, due to wearing of the brake lining in a drum brake. The strut device 10 is composed of a first and a second strut members 11 and 12 and a connecting member 13 linking both, which is a rod of circular cross-section having a star-wheel in the middle thereof, and is provided with an internally threaded portion or tapped hole 13b on one end.
The first strut member 11 is provided with a rectangular cut-out 11a on one ned thereof for engaging with the web of a brake shoe and a threaded hole 11b on the other end for threadedly engaging with the threaded portion 13b of the connecting member 13, while the second strut member 12 is provided with a rectangular cut-out 12a on one end thereof for engaging with the web of another brake shoe and a bore 12b on the other end for rotatably receiving the opposite end portion from the threaded portion 13b of the connecting member 13.
When the star-wheel 13a is in the strut device 10 of such a construction, rotated manually or by means of an adjustor lever such as a hand brake lever (not shown), the strut device 10 is elongated by the moving action taking place between the internally threaded portion 11b and the externally threaded portion 13b, and the shoe clearance is thereby adjusted.
The first and second strut members 11, 12 are relatively, in general, complicated in configuration due to their mechanical function(s). The first strut member 11 is, for example, engaged with the web portion of the brake shoe by the cut-out 11a thereof; and the former and the latter rotate relatively to each other, when the brake is operated, in a parallel direction to the plane of the drawing paper in FIG. 1, only a slight angle, though. When the dimension W in FIG. 1 is large, the brake shoe web and the first strut member can not rotate smoothly. The dimension W is, therefore, required to be small to the greatest possible extent. The width S of the end portion of the strut device 10 for engaging with the web portion of the brake shoe is desired, on the contrary, to be as large as possible from the view point of the length adjusting function of the strut device 10; because the wider width S will easier prevent the first strut member 11 from rotating with the connecting member. As a result of this the first strut member 11 is obliged to be of such an intricate configuration, as shown in FIG. 1, that is becomes once narrow in width (W) and then expands (S) again.
The second strut member 12 is also inevitable to be of complicated configuration, as shown in FIG. 2, being provided with a projection 12c for engaging with the adjust lever (not shown) to oscillate the same.
In the conventional manufacturing method both the first strut member 11 and the second strut member 12 have been, therefore, made of a forged material of high cost and then worked by a time-consuming machining process.
One of the co-inventors of the present invention developed before a manufacturing method of the first strut member 11, as shown in FIGS. 3 and 4, from a tube material; and another inventor offered similarly a manufacturing method of the second strut member 12 as shown in FIGS. 5 and 6. It has been attained to drastically decrease the production cost of the strut members by these inventions.
The principal object of the present invention is to provide a further improved method of manufacturing of the strut members.
Prior to the description of the preferred embodiments of this invention, more detailed explanation of the abovementioned manufacturing method of the strut members will be stated for better understanding of this invention.
The first strut member 11' shown in FIGS. 3 and 4 is formed by (1) pressing flat a part of a tube material in the diametrical direction, at a portion a predetermined distance apart from one extremity toward the central portion, to shape a flat plate-like portion 11'c (hereinafter simply referred to as a flat portion); (2) making a cut-out 11'a parallelly to the tube axis and perpendicularly to the flat portion 11'c, ranging from the right extremity of the tube to a part of the flat portion 11'c; and (3) making a threaded bore 11'b on the inner surface of the tube at the other end. This article was once thought a great success having satisfied the aforementioned requirements.
The second strut member 12' is formed, as shown in FIGS. 5 and 6, by (1) pressing flat one end portion of a tube material in the diametrical direction into a flat portion; and (2) forming a cut-out 12'a in the flat portion parallelly to the tube axis and another cut-out 12'c perpendicularly to the tube axis. By modifying the conventional method of forming a projection 12c on the second strut member 12, for engaging with the adjust lever by being received in an aperture thereof, into a new method of forming a cut-out in the second strut member 12' for receiving a projection disposed on the adjust lever in order to engage therewith, the manufacturing of the second strut member from a tube material was successful.